The Nature of Matter

In the preceding chapter we agreed, though without being able to find demonstrative reasons, that it is rational to believe that our sense-data—for example, those which we regard as associated with my table—are really signs of the existence of something independent of us and our perceptions. That is to say, over and above the sensations of colour, hardness, noise, and so on, which make up the appearance of the table to me, I assume that there is something else, of which these things are appearances. The colour ceases to exist if I shut my eyes, the sensation of hardness ceases to exist if I remove my arm from contact with the table, the sound ceases to exist if I cease to rap the table with my knuckles. But I do not believe that when all these things cease the table ceases. On the contrary, I believe that it is because the table exists continuously that all these sense-data will reappear when I open my eyes, replace my arm, and begin again to rap with my knuckles. The question we have to consider in this chapter is: What is the nature of this real table, which persists independently of my perception of it?

In the previous chapter, we agreed that a certain belief is rational, though we could not find conclusive reasons for it. The belief is that our sense-data are signs of something that exists independently of us and our perceptions. Examples include the sense-data we associate with my table. In other words, sensations of colour, hardness, sound, and so on make up the table’s appearance to me. I assume there is something beyond these sensations, something they are appearances of. The colour stops existing if I close my eyes. The sensation of hardness stops existing if I move my arm away from the table. The sound stops existing if I stop tapping the table with my knuckles. But I do not believe that the table stops existing when all these sensations stop. On the contrary, I believe the table’s continued existence explains why all these sense-data will return. They will return when I open my eyes, put my arm back, and start tapping again with my knuckles. The question we must consider in this chapter is: What is the nature of this real table, which continues to exist independently of my perception of it?

To this question physical science gives an answer, somewhat incomplete it is true, and in part still very hypothetical, but yet deserving of respect so far as it goes. Physical science, more or less unconsciously, has drifted into the view that all natural phenomena ought to be reduced to motions. Light and heat and sound are all due to wave-motions, which travel from the body emitting them to the person who sees light or feels heat or hears sound. That which has the wave-motion is either aether or 'gross matter', but in either case is what the philosopher would call matter. The only properties which science assigns to it are position in space, and the power of motion according to the laws of motion. Science does not deny that it may have other properties; but if so, such other properties are not useful to the man of science, and in no way assist him in explaining the phenomena.

Physical science offers an answer to this question. The answer is somewhat incomplete and still partly hypothetical, but deserves respect as far as it goes. More or less unconsciously, physical science has drifted toward the view that all natural phenomena should be reduced to motion. Light, heat, and sound are all caused by wave motions. These waves travel from the body emitting them to the person who sees light, feels heat, or hears sound. The substance carrying the waves is either aether or 'gross matter'. In either case, a philosopher would call the substance matter. The only properties science assigns to matter are position in space and the ability to move according to the laws of motion. Science does not deny that matter may have other properties. But if matter has other properties, those properties are not useful to scientists and do nothing to help explain the phenomena.

It is sometimes said that 'light is a form of wave-motion', but this is misleading, for the light which we immediately see, which we know directly by means of our senses, is not a form of wave-motion, but something quite different—something which we all know if we are not blind, though we cannot describe it so as to convey our knowledge to a man who is blind. A wave-motion, on the contrary, could quite well be described to a blind man, since he can acquire a knowledge of space by the sense of touch; and he can experience a wave-motion by a sea voyage almost as well as we can. But this, which a blind man can understand, is not what we mean by light: we mean by light just that which a blind man can never understand, and which we can never describe to him.

People sometimes say that 'light is a form of wave-motion', but this is misleading. The light we see directly, which we know through our senses, is not a form of wave-motion. It is something quite different. We all know this light if we are not blind. But we cannot describe it in a way that conveys our knowledge to someone who is blind. Wave-motion, by contrast, could easily be described to a blind person, who can learn about space through touch. A blind person can also experience wave-motion on a sea voyage almost as well as we can. But wave-motion, which a blind person can understand, is not what we mean by light. By light, we mean precisely what a blind person can never understand and what we can never describe to them.

Now this something, which all of us who are not blind know, is not, according to science, really to be found in the outer world: it is something caused by the action of certain waves upon the eyes and nerves and brain of the person who sees the light. When it is said that light is waves, what is really meant is that waves are the physical cause of our sensations of light. But light itself, the thing which seeing people experience and blind people do not, is not supposed by science to form any part of the world that is independent of us and our senses. And very similar remarks would apply to other kinds of sensations.

Now, according to science, the light that all of us who are not blind experience is not actually in the outside world. Instead, certain waves produce this experience by acting on the eyes, nerves, and brain of the person seeing the light. When we say that light is waves, we really mean that waves physically cause our sensations of light. But light itself is what people who can see experience and blind people do not. Science does not regard light itself as part of a world independent of us and our senses. And very similar points would apply to other kinds of sensations.

It is not only colours and sounds and so on that are absent from the scientific world of matter, but also space as we get it through sight or touch. It is essential to science that its matter should be in a space, but the space in which it is cannot be exactly the space we see or feel. To begin with, space as we see it is not the same as space as we get it by the sense of touch; it is only by experience in infancy that we learn how to touch things we see, or how to get a sight of things which we feel touching us. But the space of science is neutral as between touch and sight; thus it cannot be either the space of touch or the space of sight.

Colours, sounds, and similar qualities are absent from the scientific world of matter. So is space as we experience it through sight or touch. Science requires matter to exist in a space. But that space cannot be exactly the space we see or feel. To begin with, space as we see it differs from space as we experience it through touch. Only through experience in infancy do we learn how to touch things we see. Through that same experience, we learn how to see things we feel touching us. But scientific space is neutral between touch and sight. So scientific space cannot be either the space we experience through touch or the space we experience through sight.

Again, different people see the same object as of different shapes, according to their point of view. A circular coin, for example, though we should always judge it to be circular, will look oval unless we are straight in front of it. When we judge that it is circular, we are judging that it has a real shape which is not its apparent shape, but belongs to it intrinsically apart from its appearance. But this real shape, which is what concerns science, must be in a real space, not the same as anybody's apparent space. The real space is public, the apparent space is private to the percipient. In different people's private spaces the same object seems to have different shapes; thus the real space, in which it has its real shape, must be different from the private spaces. The space of science, therefore, though connected with the spaces we see and feel, is not identical with them, and the manner of its connexion requires investigation.

Again, the same object appears to have different shapes to different people, depending on their viewpoint. For example, although we would always judge a circular coin to be circular, the coin will usually look oval. The exception is when we are directly in front of the coin. When we judge that the coin is circular, we judge that the coin has a real shape. This real shape differs from its apparent shape and belongs to the coin itself, regardless of how the coin appears. But this real shape, which science studies, must exist in a real space, different from anyone’s apparent space. Real space is shared, while apparent space is private to the person perceiving it. The same object seems to have different shapes in different people’s private spaces. So the real space, where the object has its real shape, must differ from those private spaces. The space of science, therefore, is connected with the spaces we see and feel, but is not identical to them. How these spaces are connected needs investigation.

We agreed provisionally that physical objects cannot be quite like our sense-data, but may be regarded as causing our sensations. These physical objects are in the space of science, which we may call 'physical' space. It is important to notice that, if our sensations are to be caused by physical objects, there must be a physical space containing these objects and our sense-organs and nerves and brain. We get a sensation of touch from an object when we are in contact with it; that is to say, when some part of our body occupies a place in physical space quite close to the space occupied by the object. We see an object (roughly speaking) when no opaque body is between the object and our eyes in physical space. Similarly, we only hear or smell or taste an object when we are sufficiently near to it, or when it touches the tongue, or has some suitable position in physical space relatively to our body. We cannot begin to state what different sensations we shall derive from a given object under different circumstances unless we regard the object and our body as both in one physical space, for it is mainly the relative positions of the object and our body that determine what sensations we shall derive from the object.

We tentatively agreed that physical objects cannot be quite like our sense-data, but we may regard them as causing our sensations. These physical objects exist in the space of science, which we may call 'physical' space. One point is important: if physical objects cause our sensations, physical space must contain more than those objects. It must also contain our sense organs, nerves, and brain. We feel an object through touch when we are in contact with it. In other words, some part of our body occupies a place in physical space very close to the object. Roughly speaking, we see an object when no opaque body lies between the object and our eyes in physical space. Similarly, we can hear, smell, or taste an object only under certain conditions. We must be close enough to the object, or the object must touch our tongue. Or the object must occupy some suitable position in physical space relative to our body. We cannot begin to describe the different sensations an object will give us under different circumstances without a shared physical space. We must regard both the object and our body as being in that space. This is because their relative positions mainly determine the sensations we get from the object.

Now our sense-data are situated in our private spaces, either the space of sight or the space of touch or such vaguer spaces as other senses may give us. If, as science and common sense assume, there is one public all-embracing physical space in which physical objects are, the relative positions of physical objects in physical space must more or less correspond to the relative positions of sense-data in our private spaces. There is no difficulty in supposing this to be the case. If we see on a road one house nearer to us than another, our other senses will bear out the view that it is nearer; for example, it will be reached sooner if we walk along the road. Other people will agree that the house which looks nearer to us is nearer; the ordnance map will take the same view; and thus everything points to a spatial relation between the houses corresponding to the relation between the sense-data which we see when we look at the houses. Thus we may assume that there is a physical space in which physical objects have spatial relations corresponding to those which the corresponding sense-data have in our private spaces. It is this physical space which is dealt with in geometry and assumed in physics and astronomy.

Our sense-data exist in our private spaces: the space of sight, the space of touch, or vaguer spaces provided by other senses. Science and common sense assume there is one shared physical space containing all physical objects. If so, the relative positions of physical objects must roughly match the relative positions of sense-data in our private spaces. There is no difficulty in supposing that these positions match. If we see one house on a road as nearer to us than another, our other senses will confirm this impression. For example, we will reach the nearer house sooner if we walk along the road. Other people will agree that the house that looks nearer to us is nearer. A survey map will show the same thing. So everything points to a spatial relationship between the houses matching the relationship between the sense-data we see when looking at them. We may therefore assume that there is a physical space in which physical objects have spatial relationships. These relationships correspond to those between the matching sense-data in our private spaces. This physical space is the subject of geometry and is assumed in physics and astronomy.

Assuming that there is physical space, and that it does thus correspond to private spaces, what can we know about it? We can know only what is required in order to secure the correspondence. That is to say, we can know nothing of what it is like in itself, but we can know the sort of arrangement of physical objects which results from their spatial relations. We can know, for example, that the earth and moon and sun are in one straight line during an eclipse, though we cannot know what a physical straight line is in itself, as we know the look of a straight line in our visual space. Thus we come to know much more about the relations of distances in physical space than about the distances themselves; we may know that one distance is greater than another, or that it is along the same straight line as the other, but we cannot have that immediate acquaintance with physical distances that we have with distances in our private spaces, or with colours or sounds or other sense-data. We can know all those things about physical space which a man born blind might know through other people about the space of sight; but the kind of things which a man born blind could never know about the space of sight we also cannot know about physical space. We can know the properties of the relations required to preserve the correspondence with sense-data, but we cannot know the nature of the terms between which the relations hold.

Assuming physical space exists and corresponds to our private spaces in this way, what can we know about physical space? We can know only what is needed to ensure that correspondence. In other words, we cannot know what physical space is like in itself. But we can know how physical objects are arranged through their spatial relations. For example, we can know that the earth, moon, and sun lie in one straight line during an eclipse. Yet we cannot know what a physical straight line is in itself. By contrast, we do know how a straight line looks in our visual space. So we know much more about the relations between distances in physical space than about the distances themselves. We may know that one distance is greater than another, or lies along the same straight line as another. But we cannot know physical distances as directly as we know distances in our private spaces. Nor can we know physical distances as directly as we know colours, sounds, or other sense-data. We can know everything about physical space that someone born blind might learn from others about visual space. But whatever someone born blind could never know about visual space, we also cannot know about physical space. We can know the properties of the relations needed to maintain the correspondence with sense-data. But we cannot know the nature of the things connected by those relations.

With regard to time, our feeling of duration or of the lapse of time is notoriously an unsafe guide as to the time that has elapsed by the clock. Times when we are bored or suffering pain pass slowly, times when we are agreeably occupied pass quickly, and times when we are sleeping pass almost as if they did not exist. Thus, in so far as time is constituted by duration, there is the same necessity for distinguishing a public and a private time as there was in the case of space. But in so far as time consists in an order of before and after, there is no need to make such a distinction; the time-order which events seem to have is, so far as we can see, the same as the time-order which they do have. At any rate no reason can be given for supposing that the two orders are not the same. The same is usually true of space: if a regiment of men are marching along a road, the shape of the regiment will look different from different points of view, but the men will appear arranged in the same order from all points of view. Hence we regard the order as true also in physical space, whereas the shape is only supposed to correspond to the physical space so far as is required for the preservation of the order.

Our feeling of how long time lasts or how much time has passed is notoriously unreliable compared with a clock. Time passes slowly when we are bored or in pain, and quickly when we are pleasantly occupied. When we sleep, time passes almost as if it did not exist. So, when we consider time as duration, we must distinguish between public and private time, just as with space. But when we consider time as an order of before and after, we need no such distinction. As far as we can see, events seem to occur in the same order as they actually do. At any rate, we can give no reason to suppose that the apparent and actual orders differ. The same is usually true of space. If a regiment of men marches along a road, the regiment's shape will look different from different viewpoints. But the men will appear arranged in the same order from every viewpoint. So we regard this order as also holding in physical space. By contrast, we suppose the apparent shape corresponds to physical space only as far as needed to preserve that order.

In saying that the time-order which events seem to have is the same as the time-order which they really have, it is necessary to guard against a possible misunderstanding. It must not be supposed that the various states of different physical objects have the same time-order as the sense-data which constitute the perceptions of those objects. Considered as physical objects, the thunder and lightning are simultaneous; that is to say, the lightning is simultaneous with the disturbance of the air in the place where the disturbance begins, namely, where the lightning is. But the sense-datum which we call hearing the thunder does not take place until the disturbance of the air has travelled as far as to where we are. Similarly, it takes about eight minutes for the sun's light to reach us; thus, when we see the sun we are seeing the sun of eight minutes ago. So far as our sense-data afford evidence as to the physical sun they afford evidence as to the physical sun of eight minutes ago; if the physical sun had ceased to exist within the last eight minutes, that would make no difference to the sense-data which we call 'seeing the sun'. This affords a fresh illustration of the necessity of distinguishing between sense-data and physical objects.

When we say events seem to occur in the same order as they really do, we must avoid a possible misunderstanding. The states of different physical objects need not occur in the same order as our sense-data from perceiving those objects. As physical events, thunder and lightning happen at the same time. That is, lightning happens at the same time as the disturbance in the air where the lightning occurs. But the sense-datum we call hearing thunder occurs only when the disturbance in the air reaches us. Similarly, the sun's light takes about eight minutes to reach us. So when we see the sun, we see the sun as it was eight minutes ago. To the extent that our sense-data provide evidence about the physical sun, that evidence concerns the sun eight minutes ago. If the physical sun had ceased to exist within the last eight minutes, our sense-data would be no different. We would still have the sense-data we call 'seeing the sun'. This example further illustrates why we must distinguish between sense-data and physical objects.

What we have found as regards space is much the same as what we find in relation to the correspondence of the sense-data with their physical counterparts. If one object looks blue and another red, we may reasonably presume that there is some corresponding difference between the physical objects; if two objects both look blue, we may presume a corresponding similarity. But we cannot hope to be acquainted directly with the quality in the physical object which makes it look blue or red. Science tells us that this quality is a certain sort of wave-motion, and this sounds familiar, because we think of wave-motions in the space we see. But the wave-motions must really be in physical space, with which we have no direct acquaintance; thus the real wave-motions have not that familiarity which we might have supposed them to have. And what holds for colours is closely similar to what holds for other sense-data. Thus we find that, although the relations of physical objects have all sorts of knowable properties, derived from their correspondence with the relations of sense-data, the physical objects themselves remain unknown in their intrinsic nature, so far at least as can be discovered by means of the senses. The question remains whether there is any other method of discovering the intrinsic nature of physical objects.

What we have found about space is much like what we find about how sense-data correspond to physical objects. If one object looks blue and another red, we may reasonably assume some corresponding difference between the physical objects. If two objects both look blue, we may assume a corresponding similarity. But we cannot hope to know directly the quality in a physical object that makes the object look blue or red. Science tells us that this quality is a certain kind of wave motion. Wave motion sounds familiar because we think of waves moving in the space we see. But these waves must actually move in physical space, which we do not know directly. So the actual wave motions are not as familiar as we might have supposed. What is true of colours is much like what is true of other sense-data. So we find that the relations between physical objects have all sorts of properties we can know. We can know these properties because the relations between physical objects correspond to the relations between sense-data. Although we can know these relations, the inner nature of physical objects themselves remains unknown. At least, their inner nature remains unknown as far as our senses can reveal. The question remains whether there is any other way to discover the inner nature of physical objects.

The most natural, though not ultimately the most defensible, hypothesis to adopt in the first instance, at any rate as regards visual sense-data, would be that, though physical objects cannot, for the reasons we have been considering, be exactly like sense-data, yet they may be more or less like. According to this view, physical objects will, for example, really have colours, and we might, by good luck, see an object as of the colour it really is. The colour which an object seems to have at any given moment will in general be very similar, though not quite the same, from many different points of view; we might thus suppose the 'real' colour to be a sort of medium colour, intermediate between the various shades which appear from the different points of view.

The most natural starting assumption, at least about visual sense-data, is not ultimately the most defensible one. For the reasons we have considered, physical objects cannot be exactly like sense-data, but they may be somewhat similar. According to this view, physical objects really do have colours, for example. By good luck, we might see an object as having the colour it really has. At any given moment, an object's apparent colour will generally be very similar from many different viewpoints. But the colour will not be quite the same from each viewpoint. We might therefore suppose that the 'real' colour is a kind of middle colour, between the shades seen from different viewpoints.

Such a theory is perhaps not capable of being definitely refuted, but it can be shown to be groundless. To begin with, it is plain that the colour we see depends only upon the nature of the light-waves that strike the eye, and is therefore modified by the medium intervening between us and the object, as well as by the manner in which light is reflected from the object in the direction of the eye. The intervening air alters colours unless it is perfectly clear, and any strong reflection will alter them completely. Thus the colour we see is a result of the ray as it reaches the eye, and not simply a property of the object from which the ray comes. Hence, also, provided certain waves reach the eye, we shall see a certain colour, whether the object from which the waves start has any colour or not. Thus it is quite gratuitous to suppose that physical objects have colours, and therefore there is no justification for making such a supposition. Exactly similar arguments will apply to other sense-data.

Such a theory perhaps cannot be conclusively disproved, but it can be shown to have no basis. To begin with, the colour we see clearly depends only on the nature of the light waves striking the eye. So the colour is affected by whatever lies between us and the object. It is also affected by how light reflects off the object towards the eye. The air between us and the object changes colours unless the air is perfectly clear. Any strong reflection will change the colours completely. Thus the colour we see results from the light ray as it reaches the eye. The colour is not simply a property of the object the ray comes from. So, provided certain waves reach the eye, we will see a certain colour. We will see that colour whether or not the object the waves come from has any colour itself. Thus, assuming that physical objects have colours is entirely unwarranted, and there is no justification for such an assumption. Exactly similar arguments apply to other sense-data.

It remains to ask whether there are any general philosophical arguments enabling us to say that, if matter is real, it must be of such and such a nature. As explained above, very many philosophers, perhaps most, have held that whatever is real must be in some sense mental, or at any rate that whatever we can know anything about must be in some sense mental. Such philosophers are called 'idealists'. Idealists tell us that what appears as matter is really something mental; namely, either (as Leibniz held) more or less rudimentary minds, or (as Berkeley contended) ideas in the minds which, as we should commonly say, 'perceive' the matter. Thus idealists deny the existence of matter as something intrinsically different from mind, though they do not deny that our sense-data are signs of something which exists independently of our private sensations. In the following chapter we shall consider briefly the reasons—in my opinion fallacious—which idealists advance in favour of their theory.

One question remains: are there any general philosophical arguments showing what matter must be like, if matter is real? As explained above, very many philosophers, perhaps most, have held that everything real must be mental in some sense. Or at least, anything we can know anything about must be mental in some sense. Such philosophers are called 'idealists'. Idealists tell us that what appears to be matter is really something mental. For Leibniz, matter consists of more or less rudimentary minds. For Berkeley, matter consists of ideas in minds that, as we would ordinarily say, 'perceive' matter. Thus idealists deny that matter exists as something fundamentally different from mind. But idealists do not deny that our sense-data are signs of something existing independently of our private sensations. In the next chapter, we will briefly consider the reasons idealists give in support of their theory. In my opinion, those reasons are flawed.